a) Field of the Invention
The present invention relates to a micro dimension electronic device, and more particularly to a micro dimension electronic device using semiconductor quantum dot. Here, the term "micro" means "very small" and usually expresses a dimension less than the order of micron.
b) Description of the Related Art
In recent years, associated with a progress of techniques on fine processing, micro dimension electronic devices including portions of such dimensions as generating quantum effects are starting to be manufactured.
Elements having such structures that confine carriers of charge in a one-dimensional direction as quantum well, in two-dimensional directions as quantum wire, in three-dimensional directions as quantum dot, or the like, have been manufactured. For such elements, not a small number of new phenomena which have been impossible to be attained in conventional devices are being found. Researches to work out new devices or systems using such phenomena are being focused.
Such a quantum effect device, having a micro dimension, generates an output signal which is also very small. Consequently, a serious problem arise how to take out signal from the inside of the device to an external circuit.
Electron devices using quantum dot can be considered to have a function of carrying out a logical operation or of storing a memory by utilizing an in/out behavior of a single electron to the quantum dot. Even when such function can be performed, it is, however, difficult to practically utilize the phenomenon unless detection of the state, for example, detecting a change in the number of electrons within a quantum dot, is made possible.
A method that detects a change of electric potential in a quantum dot by electrically connecting a gate electrode of an insulated gate type field effect transistor to the quantum dot could be considered. In connecting the gate electrode of a field effect transistor of the actual size to the quantum dot, however,parasitic capacitance of the quantum dot becomes so large, that a change in electric potential when a single electron moves into and out of the quantum dot becomes so small to be detected under thermal noise even at a considerable low temperature.
When a plurality of electrodes are disposed in the vicinity of a quantum well layer and depletion layers are developed into the quantum well by application of reverse bias voltage to the electrodes, a plurality of quantum dots can be formed within a quantum well layer. By connecting an electrode associated with a quantum dot with another electrode associated with another quantum dot, the voltage of a quantum dot can be transferred to another quantum dot. In this case, when there is a current flow in the other quantum dot, a change in voltage can be converted to a change in current.
However, considering this kind of signal transfer as the change in voltage, only a change in voltage of at most the order of mV is converted to a change in voltage at most of the order of mV. Thus, no solution is given to the problem of how to take out an output signal to the external circuit.
Thus, in an electronic device using quantum dot, it has been difficult to take out a state of quantum dot to an external circuit as an electric signal. It has been particularly difficult to detect the change in number of electron within a quantum dot.